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Stock-Based Compensation (Restricted Stock Units) (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Jan. 03, 2017
Restricted Stock Units (RSUs) [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]        
Nonvested, shares, beginning balance 0      
Nonvested, weighted-average grant date fair value, beginning balance (in dollars per share) $ 0.00      
Granted, shares [1] 632,255      
Granted, weighted-average grant date fair value (in dollars per share) $ 43.66 [1] $ 58.69 $ 60.04  
Vested, shares (45,657)      
Vested, weighted-average grant date fair value (in dollars per share) $ 49.28      
Forfeited, shares (66,989)      
Forfeited, weighted-average grant date fair value (in dollars per share) $ 43.30      
Nonvested, shares, ending balance 519,609 0    
Nonvested, weighted-average grant date fair value, ending balance (in dollars per share) $ 43.22 $ 0.00    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]        
Total fair value of RSU's vested $ 2.2 $ 2.3 $ 2.7  
Granted, weighted-average grant date fair value (in dollars per share) $ 43.66 [1] $ 58.69 $ 60.04  
Director [Member] | Restricted Stock Units (RSUs) [Member] | Non-Employee Director Equity Plan 2014 [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of restricted stock units granted to each non-employee director       5,073
Employee [Member] | Employee Equity and Incentive Plan 2017 [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Measurement Period Performance-Based Restricted Stock Units 1 year      
Employee [Member] | Time-based Restricted Stock Units [Member] | Employee Equity and Incentive Plan 2017 [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period (in years) 4 years      
Employee [Member] | Performance-based Restricted Stock Units Graded Vesting [Member] | Employee Equity and Incentive Plan 2017 [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period (in years) 4 years      
Employee [Member] | Performance-based Restricted Stock Units Cliff Vesting [Member] | Employee Equity and Incentive Plan 2017 [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period (in years) 3 years      
Measurement Period Additional Performance Metric Selected Performance-Based Restricted Stock Units 3 years      
[1] The RSUs granted during 2017 are primarily related to our employee annual equity award grant in April 2017 and non-employee director annual equity award grant in January 2017.